Immune Responses to Defined Antigens of Mycobacterium bovis in Cattle Experimentally Infected with Mycobacterium kansasii

Cross-reactive responses elicited by exposure to nontuberculous mycobacteria often confound the interpretation of antemortem tests for Mycobacterium bovis infection of cattle. The use of specific proteins (e.g., ESAT-6, CFP-10, and MPB83), however, generally enhances the specificity of bovine tuberculosis tests. While genes for these proteins are absent from many nontuberculous mycobacteria, they are present in M. kansasii. Instillation of M. kansasii into the tonsillar crypts of calves elicited delayed-type hypersensitivity and in vitro gamma interferon and nitrite concentration responses of leukocytes to M. avium and M. bovis purified protein derivatives (PPDs). While the responses of M. kansasii-inoculated calves to M. avium and M. bovis PPDs were approximately equivalent, the responses of M. bovis-inoculated calves to M. bovis PPD exceeded their respective responses to M. avium PPD. The gamma interferon and nitrite responses of M. kansasii-inoculated calves to recombinant ESAT-6‐CFP-10 (rESAT-6‐CFP-10) exceeded corresponding responses of noninoculated calves as early as 15 and 30 days after inoculation, respectively, and persisted throughout the study. The gamma interferon and nitrite responses of M. bovis-inoculated calves to rESAT-6‐CFP-10 exceeded the corresponding responses of M. kansasii-inoculated calves beginning 30 days after inoculation. By using a lipoarabinomannanbased enzyme-linked immunosorbent assay, specific serum antibodies were detected as early as 50 days after challenge with M. kansasii. By a multiantigen print immunoassay and immunoblotting, serum antibodies to MPB83, but not ESAT-6 or CFP-10, were detected in M. kansasii-inoculated calves; however, responses to MPB83 were notably weaker than those elicited by M. bovis infection. These findings indicate that M. kansasii infection of calves elicits specific responses that may confound the interpretation of bovine tuberculosis tests. Mycobacterium bovis, a member of the M. tuberculosis complex, has a wide host range, is infectious to humans, and is the most common cause of tuberculosis (TB) in cattle. The presence of wildlife reservoirs (e.g., various deer species in the United Kingdom and the United States, the Eurasian badger in the United Kingdom, and brush-tailed possums in New Zealand) hinder efforts to eradicate TB within cattle and captive deer herds in developed countries. In Africa, bovine TB is rapidly spreading through Cape buffalo populations as well as other hoofstock, nonhuman primates, and various mammalian predators (23). Most notably, up to 90% of lions in areas of TB endemicity are M. bovis infected, likely due to infection rate amplification from predation on infected prey. In humans, recent TB outbreaks in several U.S. cities are linked with the ingestion of M. bovis-infected, nonpasteurized cheese from Mexico (47). Regardless of the host, the implications of TB diagnosis include regulatory action, public health concerns, movement restriction, isolation of affected individuals, and serious health issues, thus emphasizing the need for accurate diagnosis. The tests most widely used for the detection of TB